1. Field of the Invention
The present invention relates to a flame-retardant thermoplastic resin composition, more precisely, to a flame-retardant thermoplastic resin composition and its moldings having the advantages of good impact resistance, good oil resistance, good heat stability and good recyclability. The invention also relates to a flame-retardant polycarbonate resin composition, in particular to that having good moldability and good heat stability and therefore suitable to injection molding to give thin-walled or large-sized moldings, and relates to moldings of the resin composition as produced by molding the resin composition through injection molding. Favorably, the polycarbonate resin composition is molded through injection molding in hot runner molds to give moldings having good outward appearances.
2. Description of the Related Art
As having the advantages of impact resistance, heat resistance and good electric properties, polycarbonate resins have many applications in various fields of, for example, office automation appliances, electric and electronic appliances, car parts and building materials. However, there are some problems with polycarbonate resins in that they require high molding and working temperatures and their melt fluidity is low. Therefore, they require relatively high molding temperatures. In particular, when various additives are added thereto, their thermal stability is often lowered, and, in addition, they could not often exhibit their good properties.
As a rule, polycarbonate resins are self-extinguishable. However, some of their applications to office automation appliances, electric and electronic appliances and others require high-level flame retardancy. To meet the requirement, various flame retardants are added to polycarbonate resins.
On the other hand, moldings for parts and housings for office automation appliances such as duplicators and facsimiles and for other electric and electronic appliances such as those mentioned above shall have a complicated shape with local projections or depressions, for example, having ribs or bosses therewith, and are required to be lightweight and thin-walled from the viewpoint of resources saving. Therefore, desired are polycarbonate resin compositions having increased melt fluidity, or that is, having increased injection moldability.
On the other hand, compositions of polycarbonate resins to which are added styrene resins such as acrylonitrile-butadiene-styrene resins (ABS resins), a rubber-modified styrenic resin (HIPS), acrylonitrile-styrene resins (AS resins) and the like are known as polymer alloys, and have many applications in the field of moldings as having good heat resistance and impact resistance.
For improving the flame retardancy of polycarbonate resins, halogenxe2x80x94containing flame retardants such as bisphenol A halides and halogenated polycarbonate oligomers have been used along with a flame retardation promoter such as antimony oxide, as their flame-retarding ability is good. However, with the recent tendency toward safety living and environmental protection, the market requires flame retardation with non-halogen flame retardants. As non-halogen flame retardants, phosphorusxe2x80x94containing organic flame retardants, especially organic phosphate ester compounds may be added to polycarbonate resin compositions, for which various methods have been proposed. Such flame retardants, organic phosphate ester compounds serve also as a plasticizer, and polycarbonate resin compositions containing them exhibit excellent flame retardancy.
To meet the requirements as above, various methods have heretofore been proposed. Concretely, JP-A 61-55145 discloses a thermoplastic resin composition comprising (A) an aromatic polycarbonateresin, (B) an ABS resin, (C) an AS resin, (D) a halogen compound, (E) a phosphate, and (F) a polytetrafluoroethylene component. JP-A 2-32154 discloses a molding polycarbonate composition with high flame retardancy and high impact resistance, comprising (A) an aromatic polycarbonate resin, (B) an ABS resin, (C) an AS resin, (D) a phosphate, and (E) a polytetrafluoroethylene component. JP-A 8-239565 discloses a polycarbonate resin composition comprising (A) an aromatic polycarbonate, (B) an impact-resistant polystyrene resin with rubber-like elasticity, (C) a halogen-free phosphate, (D) a core/shell-type grafted rubber-like elastomer, and (E) talc.
These are all to improve the melt fluidity and therefore the moldability of polycarbonates, and to improve the impact resistance and the flame retardancy of the moldings of polycarbonates. As having such improved properties, the polycarbonate compositions proposed are formed into various practicable moldings.
However, in order to make the compositions comprising a polycarbonate resin and a (rubber-modified) styrenic resin and having good melt fluidity have good flame retardancy by adding thereto a phosphate ester compound, a relatively large amount of the compound must be added to the compositions. Though their flame-retarding ability is good, phosphate ester compounds often cause some problems when added to resin compositions. For example, it is said that phosphate ester compounds will corrode molds used for molding resin compositions containing them, and, in addition, the compounds will lower the impact strength of resin moldings or will yellow them in high-temperature conditions or in high-humidity conditions.
On the other hand, phosphate ester compounds serve not only as a flame retardant but also as a plasticizer for resin compositions, and they could improve the melt moldability, especially the injection moldability of resin compositions containing them. Therefore, phosphate ester compounds could be excellent additives to resin compositions for improving the properties of resin compositions containing them, but are said to be confronted with some problems. For example, polycarbonate or styrenic resin compositions containing phosphate ester compounds could have good melt moldability, especially good injection moldability, but their moldings often have poor heat stability, depending on their shape and on the molds used for producing them. In particular, when the resin compositions are molded in injection molds such as hot runner molds where resin melts being molded therein reside for a while, the resulting moldings will be often yellowed or will have silver marks on their surface. Therefore, it is difficult to stably mold the resin compositions into moldings having good appearances, and some failed moldings will be inevitable. For these reasons, adding phosphate ester compounds to resin compositions is not all the time satisfactory. Moreover, the long-term stability of the resin moldings in high-temperature condition is often poor.
In addition, depending on their type, phosphate ester compounds often bloom resin moldings. To overcome this problem, proposed is using phosphate ester compounds having a high melting point. For this, also proposed is a method of specifically defining the monomer content and the impurity content of resins to be molded. However, polycarbonate resins for molding materials generally require relatively high molding temperatures, and merely selecting the type of phosphate ester compounds for them could not satisfactorily solve the problem of low heat stability of the resin moldings. These days, in particular, hot runner molds for injection molding are much used for producing thin-walled, complicated and large-sized resin moldings, and the resin moldings to be produced in such molds through injection moldings are required to have further higher heat stability.
To meet the requirement, proposed is using high-viscosity, high-melting point phosphate ester compounds, or using different types of phosphate ester compounds as combined. In this connection, for example, known are various methods such as those described in Japanese Patent Laid-Open Nos. 228426/1994, 151493/1996, 225737/1996, 337712/1996, 95610/1997 and 249768/1997. In these laid-open patent specifications, they say that not only using phosphate ester compounds having an increased viscosity, an increased melting point and/or an increased molecular weight but also combining the compounds with monomers is preferred. In the methods disclosed, however, resin compositions often have poor moldability and often could not be molded into resin moldings having satisfactory flame retardancy and good heat resistance.
In Japanese Patent Laid-Open No. 249768/1997, proposed are phosphate oligomers serving as a flame retardant for resins. The phosphate oligomers are characterized in that they are crosslinked with a residue of bisphenol A, and have a specific phosphate monomer content of at most 1% by weight and a total metal content of at most 30 ppm by weight, and that, when heated up to 300xc2x0 C. in an inert gas atmosphere at a heating rate of 100xc2x0 C./min, the weight loss therein for 20 minutes is at most 15% by weight measured through TGA (thermogravimetric analysis). However, even though phosphate ester compounds serving as a flame retardant are specifically defined for molding polycarbonate resins, the problem is still inevitable in that the moldability and the heat stability of the resin compositions could not be improved to a satisfactory degree.
For improving the melt fluidity of polycarbonate resins, known is adding polycarbonate oligomers to the resins. In this method, however, the impact resistance of the resin moldings formed is lowered. To solve this problem, Japanese Patent Laid-Open No. 298421/1998 discloses a polycarbonate resin composition containing, as a flame retardant, a phosphate ester compound, and containing a polycarbonate oligomer, a thermoplastic elastomer, and a polytetrafluoroethylene having the ability of forming fibrils. The resin composition could have improved heat resistance and improved impact resistance, but the polycarbonate oligomer added thereto is not all the time effective for improving the melt fluidity of the composition. In addition, adding the polycarbonate oligomer to the resin composition will often lower the oil resistance, the high-temperature resistance and the moisture resistance of the resin moldings. What is more, another problem not solved as yet with the polycarbonate oligomer is that the oligomer added to the resin composition much worsens recycled moldings of the composition and is therefore against the recent situation in the art that increasingly requires recycling resin products.
In the current situation as above, one object of the present invention is to provide a flame-retardant, thermoplastic resin composition exhibiting good fluidity and good heat stability while molded, and to provide its moldings. Specifically, the composition which the invention is intended to provide comprises a polycarbonate resin and a styrenic resin and contains a phosphate ester compound serving as a flame retardant, and it can be molded into moldings having good flame retardancy, good aging resistance including good heat resistance and good moisture resistance, and good recyclability. Another object of the invention is to provide a flame-retardant polycarbonate resin composition containing, as a flame retardant, a phosphate ester compound, and to provide its moldings. Specifically, the composition which the invention is intended to provide has good moldability, exhibiting good heat stability while molded and used. In particular, even in hot runner molds, the composition can be stably molded through injection molding into good moldings not yellowed and not having silver marks on their surface.
To attain the objects of the invention as above, we, the present inventors have assiduously studied for improving the moldability, the heat resistance and the moisture resistance of a thermoplastic resin composition with high fluidity that comprises a polycarbonate resin and a styrenic resin and contains a phosphate ester compound serving as a flame retardant. As a result, we have found that a resin composition comprising a specific polycarbonate resin and containing, as a flame retardant, a phosphate ester compound can have good flame retardancy and improved moldability, heat resistance and oil resistance, and that the physical properties of the moldings of the composition are worsened little and the moldings are yellowed little, even when used in high-temperature and high-humidity conditions and when recycled through melt molding. On the basis of these findings, we have completed the present invention. In addition, we have further studied a flame-retardant polycarbonate resin composition containing, as a flame retardant, a phosphate ester compound, for improving the heat resistance and other properties of the composition, and, as a result, have found that, when a specific phosphate ester compound capable of serving as a flame retardant is added to a polycarbonate resin composition, then the composition can have improved heat resistance while having good flame retardancy. We have further found that the composition has good moldability, and, even in hot runner molds, it can be well molded into moldings having good appearances, and that its moldings have good heat resistance and good moisture resistance. On the basis of these findings, we have completed the present invention.
Specifically, the first aspect of the invention is to provide the following:
(1) A flame-retardant thermoplastic resin composition comprising 100 parts by weight of a resin mixture of (A) from 50 to 99% by weight of a polycarbonate resin having a molecular weight distribution (Mw/Mn) of smaller than 3 and (B) from 1 to 50% by weight of a styrenic resin, and from 1 to 30 parts by weight of (C) a phosphate ester compound;
(2) The flame-retardant thermoplastic resin composition of above (1), wherein the resin mixture is composed of (A) from 60 to 95% by weight of the polycarbonate resin and (B) from 5 to 40% by weight of a rubber-modified styrenic resin;
(3) The flame-retardant thermoplastic resin composition of above (1) or (2), which further contains from 0.05 to 5 parts by weight, relative to 100 parts by weight of the resin mixture of (A) and (B), of (D) a fluoro-olefinic resin;
(4) The flame-retardant thermoplastic resin composition of any one of above (1) to (3), which further contains from 1 to 30 parts by weight, relative to 100 parts by weight of the resin mixture of (A) and (B), of (E) a core/shell-type, grafted rubber-like elastomer;
(5) Moldings of the flame-retardant thermoplastic resin composition of any one of above (1) to (4); and
(6) Housings or parts for electric or electronic appliances, as produced through injection molding of the flame-retardant thermoplastic resin composition of any one of above (1) to (4).
The second aspect of the invention provides the following:
(1) A flame-retardant polycarbonate resin composition comprising 100 parts by weight of a resin or resin mixture of (A) from 60 to 100% by weight of a polycarbonate resin and (B) from 0 to 40% by weight of a styrenic resin, and from 1 to 30 parts by weight of (C) a phosphate ester compound having an acid value of at most 1 mg KOH/g;
(2) The flame-retardant polycarbonate resin composition of above (1), wherein the monomer content of the phosphate ester compound is at most 3% by weight;
(3) The flame-retardant polycarbonate resin composition of above (1) or (2), wherein the resin mixture is composed of (A) from 60 to 97% by weight of a polycarbonate resin and (B) from 3 to 40% by weight of a modified styrenic resin;
(4) The flame-retardant polycarbonate resin composition of any one of above (1) to (3), which further contains from 0.05 to 5 parts by weight, relative to 100 parts by weight of the resin or resin mixture of (A) and (B), of (D) a fluoro-olefinic resin;
(5) The flame-retardant polycarbonate resin composition of any one of above (1) to (4), which further contains from 1 to 30 parts by weight, relative to 100 parts by weight of the resin or resin mixture of (A) and (B), of (E) a core/shell-type, grafted rubber-like elastomer;
(6) Moldings of the flame-retardant polycarbonate resin composition of any one of above (1) to (5);
(7) Injection moldings of the flame-retardant polycarbonate resin composition of any one of above (1) to (5), as produced through injection molding of the composition in hot runner molds; and
(8) Moldings of above (6) or (7), which are for housings or parts for electric or electronic appliances.